Light curable liquid acrylic ester adhesives for glass bonding using low intensity ultraviolet (xe2x80x9cUVxe2x80x9d) light are known. Such adhesives are useful for glass assembly and repair applications in which high intensity UV light is unavailable or impractical. Using such adhesives, broken glassware and decorative glass items can be rapidly bonded and fabricated using low intensity light sources which give output in the UV/visible wavelength region.
One problem associated with such known UV glass bonding adhesives is yellowing on storage and exposure to light during use. Another problem common with such adhesives is surface cure inhibition when cured under atmospheric conditions.
A number of fast curing low-yellowing acrylate functional oligomer products are known for use in UV/electron beam (xe2x80x9cEBxe2x80x9d) curable printing inks and the like. However, such products typically have poor adhesive strength to glass.
It would be desirable to provide an improved low intensity UV/visible curable adhesive suitable for glass bonding which provides good adhesive strength, fast tack-free time and reduced yellowing than commercially available adhesives. Desirably such adhesives should also display good humidity resistance.
The present invention is directed to low intensity UV/visible curable adhesives which provide improved low-yellowing properties with fast fixture time at low UV intensity over current glass bonding adhesives. These adhesives maintain good bond strength and durability at least comparable to known UV acrylic glass bonding adhesives. The composition of the present invention includes:
a) an aliphatic polyether urethane acrylate oligomer having an average of least 2.5 acrylate groups per molecule, suitably in an amount of 50% 75% by weight of the total composition;
b) at least one of
i) a combination of at least one aliphatic (poly)ester urethane diacrylate and at least one alkoxylated bisphenol A di(meth)acrylate; or
ii) a urethane di(meth)acrylate of alkoxylated hydrogenated bisphenol A, suitably in an amount of 5%-70% by weight of the total composition;
c) a diluent (meth)acrylate ester having an ambient viscosity of about 100-5,000 cps, suitably in an amount of 5%-60% by weight of the total composition;
d) optionally an adhesion promoter, suitably in an amount of 0.2%-30% by weight of the total composition; and
e) a photoinitiator component, suitably in an amount of 0.2%-10% by weight of the total composition.
A further aspect of the invention provides a method of glass bonding in which an adhesive composition is applied to at least one of a pair of glass substrates, and then the substrates are joined and subjected to low intensity UV radiation for sufficient time to fixture the adhesive.
For purposes of the present invention low intensity UV radiation is radiation from a broad spectrum UV or a UV/visible source, having an intensity at 365 nm of about 6 milliwatts or less per square centimeter, at the substrate surface.
The aliphatic polyether urethane acrylate compounds useful in the invention are suitably prepared by reacting an aliphatic diisocyanate with an aliphatic polyether polyol, at a ratio of about 2 or more isocyanate groups of the diisocyanate per hydroxyl group of the polyether polyol compound. The remaining isocyanate groups are then reacted with a suitable hydroxyalkyl acrylate compound to produce the acrylated oligomer. The reaction can also be run in reverse sequence, preparing acrylate functional isocyanate intermediates which are then used as capping agents for the polyether polyols. The polyether polyol has an average of at least 2.5 hydroxyl groups per molecule, typically 2.5-3.5 hydroxyl groups per molecule and preferably about 3 hydroxyl groups per molecule. The polyether repeat units may suitably be ethylene oxide (xe2x80x94C2H4Oxe2x80x94), propylene oxide (xe2x80x94C3H6Oxe2x80x94) or butylene oxide (xe2x80x94C4H8Oxe2x80x94) repeat units, or mixtures thereof. In the foregoing, propylene includes n-propylene and isopropylene, and butylene includes 1,2-butylene, 1,3-buctylene, 2-methyl-1,3-propylene and 1,4-butylene. Preferred polyols may be propoxylated glycerol or propoxylated trimethylolpropane. Examples of suitable aliphatic diisocyanate include isophorone diisocyanate, methylene-bis-cyclohexane diisocyanate and 1,6-hexane diisocyanate. Examples of suitable hydroxy functional acrylate compounds include hydroxyethyl acrylate, hydroxypropyl acrylate and other diol monoacrylate esters. A desirable commercial acrylated aliphatic polyether urethane oligomer is PHOTOMER(copyright) 6019, sold by Henkel Corp., Ambler, Pa, reported in U.S. Pat. Nos. 5,908,873 and 6,014,488 to be an aliphatic urethane acrylate oligomer from polyether polyol, isophorone diisocyanate and hydroxyethyl acrylate. Mixtures of aliphatic polyether urethane acrylate compounds may be used as this component of the inventive formulation. This aliphatic polyether urethane acrylate component is employed at an amount of about 5% to about 70%, preferably 10-40%, by weight of the composition.
The second component of the inventive compositions is a di(meth)acrylate oligomer component. The second component may be either a combination of an aliphatic polyester urethane diacrylate and an alkoxylated bisphenol A di(meth)acrylate, or a block (meth)acrylate terminated poly,ether urethane based on hydrogenated bisphenol A. This second component is suitably present in an amount from about 5% to about 70% by weight of the composition.
The aliphatic polyester urethane diacrylate suitably may, be an oligomeric compound having a viscosity at 160xc2x0 F. (71xc2x0 C.) of about 700 to 5,000 cps 1,000-5,000 mPaxc2x7s), preferably about 1,000 to about 2,500 cps (1,000-2,500 mPaxc2x7s). An example such compound is PHOTOMER(copyright) 6210 sold by Henkel Corp. The aliphatic polyester urethane diacrylate is suitably employed at an amount of about 15% to about 50%, such as 20-40%, by weight of the composition. Mixtures of aliphatic polyester urethane diacrylates may be employed.
The alkoxylated bisphenol A di(meth)acrylate compound is used in combination with the aliphatic polyester urethane diacrylate to enhance the adhesive strength of the cured formulation. Ethoxylated bisphenol A dimethacrylate compounds having 2-6 ethoxylate groups per molecule are preferred. The alkoxylated bisphenol A di(meth)acrylate compound is employed at an amount of about 5% to about 50%, preferably about 10% to about 15%, by weight of the composition.
The urethane di(meth)acrylate of hydrogenated bisphenol A may be prepared by reacting 2 moles of a diisocyanate with 1 mole of hydrogenated bisphenol A. The intermediate of this reaction is then reacted with 2 moles of 2-hydroxyethyl methacrylate to produce the desired methacrylate terminated polyurethane block resin. The diisocyanate is suitably an aromatic diisocyanate, desirably toluene diisocyanate. The block polyurethane diacrylate should be used in an amount of from about 5% to about 50% by weight of the composition.
Desirably the components a) and b), respectively are present in a relative weight ratio of from about 1:3 to about 3:1, such as about 1:1.
Liquid diluent monomers which are liquid esters, preferably acrylate and methacrylate esters having a viscosity of 100-5,000 cps (100-5,000 mPaxc2x7s), preferably 100-4,000 cps (100-4,000 mPaxc2x7s), more preferably 100-2,000 cps 200-2,000 mPaxc2x7s), are desirable to provide a satisfactory viscosity to the inventive compositions. Suitably, such (meth)acrylate monomers include mono, di, or poly(meth)acrylate compounds, examples of which are xcex2-carboxyethyl acrylate, isobornyl acrylate, n-octyl acrylate, n-decyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, ethoxyethoxyethyl acrylate, ethoxylated phenyl monoacrylate hydroxyethyl acrylate, isooctyl acrylate, n-butyl acrylate, dipropylene glycol diacrylate, tetraethylene glycol diacrylate, 1,6-hexane diol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylol propane diacrylate, trimethylol propane triacrylate, pentaerythritol tetraacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, glycerol monomethacrylate, glycerol 1,3-dimethacrylate, trimethyl cyclohexyl methacrylate, methyl triglycol methacrylate, and so forth. Some of these monomers may be found as viscosity or property modifiers in the commercial oligomer products. Mono(meth)acrylate monomers are desirable.
In general methacrylate monomers give harder scratch resistant films than acrylate monomers, but slow the cure rate. A mixture of acrylate and methacrylate monomers often achieve a satisfactory balance of formulation viscosity, cure speed and cured adhesive properties. Isobomyl acrylate is a particularly desirable monomer component as it has good low-color, low viscosity uncured properties, fast cure, relatively low shrinkage on curing and gives hard scratch and resistant films as compared to those obtained with methacrylate monomers alone. Additionally, the films also have good water resistance and adhesion characteristics. The diluent monomers are employed in an amount of about 5% to about 60% by weight of the composition, such as from about 10% to about 60% by weight of the composition. Desirable compositions employ mixtures of liquid acrylate or methacrylate diluents. For instance, desirable compositions might include 10-25% of a methacrylate ester diluent, such as hydroxyethyl methacrylate or hydroxypropyl methacrylate, and 5-25% of an acrylate ester diluent, such as isobornyl acrylate. Some compositions have from about 5% to about 25% by weight of the composition of a mixture of at least one acrylate and at least one methacrylate, such as about 10% to about 25% by weight of the composition of the blend.
The compositions preferably also include one or more adhesion promoter compounds, suitably in an total amount of from about 0.5% to about 30%, preferably about 1-10%, by weight of the composition. Such compounds generally fall into two categories, acid functional monomers such as acrylic acid or methacrylic acid, and silane adhesion promoters. The silane adhesion promoters are silane or small siloxane oligomers which contain two or more hydrolyzable groups attached to silicon and at least one organic group which is a polar group and/or free-radically polymerizable. Examples of hydrolyzable groups are alkoxy groups such as methoxy or ethoxy groups, oximes, acetoxy groups, and amino groups. Examples of organic groups which are polar groups and/or free-radically polymerizable include vinyl, allyl, methacryloxypropyl, acryloxypropyl, glycidoxyethyl, glycidoxypropyl, mercaptopropyl, epoxycyclohexyl, haloalkyl, and alkyl groups having ketone, aldehyde, carboxylate, carboxylic acid, ureide, amide, or isocyanurate groups thereon. Specific examples of such compounds include glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriacetoxysilane, and acryloxypropyltrimethoxysilane. Desirable compositions include 1-10% of an acid monomer, especially acrylic acid, and 1-5% of a silane adhesion promoter.
A photoinitiator is used to render the composition light curable. Examples of photoinitiators, which initiate under a free radical mechanism, include benzophenone, acetophenone, chlorinated acetophenone, dialkoxyacetophenones, dialkylhydroxyacetophenones, dialkylhydroxyacetophenone esters, benzoin, benzoin acetate, benzoin alkyl ethers, dimethoxybenzoin, dibenzylketone, benzoylcyclohexanol and other aromatic ketones, acyloxime esters, acylphosphine oxides, acylphosphosphonates, ketosulfides, dibenzoyldisulphides, diphenyldithiocarbonate and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide. These photoinitiators are active in the UV/visible range, approximately 250-850 nm, and preferably in the range of 300 to 450 nm so that the compositions can be cured by exposure to low intensity UV. Particularly suitable photoinitiators include IRGACURE(copyright) 184, hydroxycyclohexyl phenyl ketone, available from Ciba Specialty Chemicals in Tarrytown, N.Y. and LUCIRIN(copyright) TPO, diphenyl-2,4,6-triphenylbenzoyl phosphine oxide available from BASF Corporation in Mount Olive, N.J. Typically, the photoinitiators will be employed in an amount of 0.2 to 10%, such as 1 to 6% and desirably 3-5% by weight of the composition.
The compositions of the invention may also include an inhibitor of polymerization in an amount effective to give desired shelf stability to the composition. Suitable inhibitors are well known to those skilled in the art and include those described in the aforementioned patents which described anaerobic compositions. Metal chelators, such as ethylenediamine tetraacetate (xe2x80x9cEDTAxe2x80x9d) and 1-hydroxyethylidine-1,1-diphosphonic acid (xe2x80x9cHEDPAxe2x80x9d), and quinone type inhibitors, such as hydroquinone, methyl hydroquinone, napthaquinone and benzoquinone, are exemplary. Such inhibitors are typically employed at a level of 0.1-1.0% by weight of the composition.
An improved glass bonding adhesive in accordance with the present invention, should include the following properties:
a. UV fixture time: 5 seconds at 6 mw/cm2, 365 nm wavelength;
b. Color: Yellow Indexxe2x89xa610 for the initial cured film product, and Gardner Color:xe2x89xa61 for uncured product;
c. Torque Strength: greater than 70 ft-lb;
d. Durability on humidity aging at 120 F (49 C), 100% RH or 100xc2x0 F. (38xc2x0 C.), 100% RH; and
e. Surface cure: Tack free time (TFT)  less than 80 sec., preferably less than 40 sec., at 50 mw/cm2, 365 nm.
The invention is illustrated by the following non-limiting examples.